Honeycomb structural body and assembly thereof

ABSTRACT

A honeycomb structural body ( 1 ) is obtained by bonding, into one piece, a plurality of honeycomb segments ( 2   a,    2   b ) having a plurality of through-holes ( 6 ) surrounded by partition walls ( 10 ) and extending in the axial direction. An average wall thickness of at least one honeycomb segment ( 2   a ) not constituting the outermost peripheral surface ( 23 ) of the honeycomb structural body is larger than an average wall thickness of at least of each honeycomb segment ( 2   b ) constituting the outermost peripheral surface ( 23 ) of the honeycomb structural body. A honeycomb structural assembly is obtained by providing a material B having compressive elasticity on the outermost peripheral surface ( 23 ) of the honeycomb structural body ( 1 ) in a compressed state and thereby compression-holding the honeycomb structural body ( 1 ) in a metallic container. The honeycomb structural body and assembly have low reduction in the conversion rate, purification efficiency, regeneration efficiency, etc., during use, and are superior in durability against breakage caused by thermal stress.

BACKGROUND

The present invention relates to a honeycomb structural body used in,for example, a catalyst carrier utilizing a catalytic action, for use inan internal combustion engine, a boiler, a chemical reactor, a fuel cellreformer, etc., and a filter for capturing fine particles present in anexhaust gas; as well as to an assembly thereof. More particularly, thepresent invention relates to a honeycomb structural body which hasexcellent durability against breakage caused by thermal stress appearingtherein during its use, as well as to an assembly thereof.

Honeycomb structural bodies are in use in, for example, a carrier for acatalyst having a catalytic action, for use in an internal combustionengine, a boiler, chemical reactor, a fuel cell reformer, etc., and afilter for capturing fine particles present in an exhaust gas,particularly fine particles emitted from a diesel engine.

In the honeycomb structural body used for such a purpose, the sharptemperature change of exhaust gas or local heating makes non-uniform thetemperature distribution inside the honeycomb structural body and therehave been problems such as crack generation in the honeycomb structuralbody and the like. When the honeycomb structural body is usedparticularly as a filter for capturing a particulate substance in anexhaust gas emitted from a diesel engine, it is necessary to burn thefine carbon particles deposited on the filter to remove the particlesand regenerate the filter and, in that case, high temperatures areinevitably generated locally in the filter; as a result, this processtends to generate large thermal stress and cracks.

Hence, there have been proposed processes for producing a honeycombstructural body by bonding a plurality of individual honeycomb segmentsusing an adhesive. For example, U.S. Pat. No. 4,335,783 discloses aprocess for producing a honeycomb structural body, which comprisesbonding a large number of honeycomb parts using a discontinuousadhesive. JP-B-61-51240 proposes a heat shock-resistant rotaryregenerating heat exchanging method which comprises forming, byextrusion, matrix segments of honeycomb structural body made of aceramic material, firing them, making smooth, by processing, the outerperipheral portions of the fired segments, coating the to-be-bondedareas of the resulting segments with a ceramic adhesive having, whenfired, substantially the same mineral composition as the matrix segmentsand showing a difference in thermal expansion coefficient, of 0.1% orless at 800° C., and firing the coated segments. SAE article 860008 of1986 discloses a ceramic honeycomb structural body obtained by bondingcordierite honeycomb segments with a cordierite cement. JP-A-8-28246discloses a ceramic honeycomb structural body obtained by bondinghoneycomb ceramic members with an elastic sealant made of at least athree-dimensionally intertwined inorganic fiber, an inorganic binder, anorganic binder and inorganic particles.

Meanwhile, the regulation for exhaust gas has become stricter andengines have come to have higher performance. As a result, in order toachieve an improvement in combustion conditions of an engine and anincrease in purification ability of a catalyst, the temperature ofexhaust gas has increased year by year. In this connection, a higherthermal shock resistance has become required for honeycomb carriers.Therefore, even with honeycomb structural bodies such as mentionedabove, when a sharp temperature change of inflow gas takes place, and alocal heat of reaction, a local heat of combustion, etc., become largerduring use, a thermal stress applied thereto may not be sufficientlyrelaxed, cracks may appear therein and, in an extreme case, there mayoccur, for example, disintegration of the honeycomb structural body andbreakage of the structural body into fine pieces caused by vibration.

In order to solve these problems, there is a method of allowing ahoneycomb structural body to have a large heat capacity, thereby makingsmall the temperature change, and reducing the reaction rate and thecombustion rate, lowering the maximum temperature, resulting in arelaxing of the thermal stress acting on the honeycomb structural body.Such a method, however, has had drawbacks of reductions in the reactionrate, purification efficiency and regeneration efficiency of a honeycombstructural body. In JP-B-54-110189 is proposed a honeycomb structuralbody in which the wall thickness of the honeycomb carrier is madesmaller regularly in the cross-section toward the sectional center; andin JP-A-54-150406 and JP-A-55-147154 is proposed a honeycomb structuralbody in which the wall thickness of outer cells is made larger than thewall thickness of inner cells. These honeycomb structural bodies havelarge resistance to external mechanical stress; however, since the wallthickness of the inner cells is small, a large thermal stress isgenerated during use of the honeycomb structural body and its durabilityis not sufficient.

The present invention has been made in view of such past situations andaims at providing a honeycomb structural body which is low in reductionsin the conversion rate, purification efficiency, regenerationefficiency, etc., during use and superior in durability against breakagecaused by thermal stress.

SUMMARY

A study was made in order to achieve the above aim. As a result, it wasfound that by suppressing a temperature increase at the center of ahoneycomb structural body and keeping high a temperature of itsperipheral portion, reductions in the efficiencies (e.g. conversionrate) of a honeycomb structural body can be kept low and the durabilityof the honeycomb structural body against thermal stress can be improved.It was further found that by dividing a honeycomb structural body intoat least an outer segment and an inner segment and making the averagewall thickness of the outer segment smaller than the average wallthickness of the inner segment, the above aim can be achieved. Thepresent invention has been completed based on these findings.

The first invention provides a honeycomb structural body obtained bybonding, into one piece, a plurality of honeycomb segments having alarge number of through-holes surrounded by partition walls andextending in the axial direction of the segment, characterized in thatan average wall thickness of at least one honeycomb segment notconstituting the outermost peripheral surface of the honeycombstructural body is larger than an average wall thickness of at least onehoneycomb segment constituting the outermost peripheral surface of thehoneycomb structural body.

In the first invention, it is preferred that a ratio of the average wallthickness of the at least one honeycomb segment constituting theoutermost peripheral surface to the average wall thickness of the atleast one honeycomb segment not constituting the outermost peripheralsurface is 0.2 to 0.9. It is also preferred that the sectional area ofthe at least one honeycomb segment not constituting the outermostperipheral surface is 9 to 81% of the sectional area of the honeycombstructural body. It is also preferred that the honeycomb structural bodyis used for purification of exhaust gas of an automobile, and it isfurther preferred that the honeycomb structural body is used as a filterfor capturing diesel particulate. It is further preferred that amaterial A having compressive elasticity, more preferably a ceramicfiber-made mat, and more preferably a non-intumescent mat composedmainly of alumina or mullite, is provided at part or the whole of thespaces between side surfaces of each two adjacent honeycomb segments. Itis further preferred that the main component of the honeycomb segmentcomprises (1) at least one kind of ceramic selected from the groupconsisting of silicon carbide, silicon nitride, cordierite, alumina,mullite, zirconia, zirconium phosphate, aluminum titanate, titania andcombinations thereof, and (2) Fe—Cr—Al, nikel, or metallic Si and SiC.

The second invention of the present invention provides a honeycombstructural assembly comprising a metallic container, the honeycombstructural body mentioned above, a material B having compressiveelasticity, wherein the material B having compressive elasticity isprovided on the outermost peripheral surface of the honeycomb structuralbody in a compressed state and whereby the honeycomb structural body iscompression-held in the metallic container.

In the second invention, the material B having compressive elasticity ispreferably a ceramic fiber-made mat, and further is preferably aheat-intumescent mat containing vermiculite or a non-intumescent matcomposed mainly of alumina or mullite. The honeycomb structural assemblyis preferably a canned assembly obtained by a stuffing method, atourniquet method, a clamshell method or a swaging method. Further, thehoneycomb structural assembly is preferably obtained by loading acatalyst on honeycomb segments and then accommodating thecatalyst-loaded honeycomb segments in a metallic container. Thehoneycomb structural assembly is preferably obtained also byaccommodating honeycomb segments in a metallic container and thenloading a catalyst on the honeycomb segments.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1( a) is a schematic sectional view showing one embodiment of thehoneycomb structural body of the present invention, and FIGS. 1( b) and1(c) are respectively enlarged views of the inner segment and outersegment in FIG. 1( a).

FIG. 2 is a schematic sectional view showing another embodiment of thehoneycomb structural body of the present invention.

FIG. 3 is a schematic sectional view showing one embodiment of thehoneycomb structural assembly of the present invention.

FIG. 4 is a partially cut-away view showing one example of the stuffingmethod used for accommodating a honeycomb structural body in a metalliccontainer.

FIG. 5 is a perspective view showing one example of the tourniquetmethod used for accommodating a honeycomb structural body in a metalliccontainer.

FIG. 6 is a perspective view showing one example of the clamshell methodused for accommodating a honeycomb structural body in a metalliccontainer.

FIG. 7 is a sectional view parallel to the direction of through-holes,showing one example of the swaging method used for accommodating ahoneycomb structural body in a metallic container.

FIG. 8 is a sectional view parallel to the direction of through-holes,showing one example of the swaging method used for accommodating ahoneycomb structural body in a metallic container.

FIG. 9 is a graph showing the result of a burning and regeneration test.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The honeycomb structural body and honeycomb structural assembly of thepresent invention are described in detail below with reference to theaccompanying drawings. However, the present invention is not restrictedto the following mode. Incidentally, in the following, “section” refersto a section vertical to the direction of through-holes unless otherwisespecified.

FIG. 1( a) is a schematic sectional view showing one embodiment of thehoneycomb structural body of the present invention. The honeycombstructural body 1 of the present invention is formed by bonding into onepiece honeycomb segments 2 a and 2 b each having a large number ofthrough-holes 6 divided by partition walls 10 shown in FIGS. 1( b) and1(c) and extending in the axial direction of the honeycomb segment.

The important characteristic of the present invention is that, as shownin FIGS. 1( b) and 1(c), the average wall thickness [see FIG. 1( b)] ofthe honeycomb segment 2 a not constituting the outermost peripheralsurface 23 of the honeycomb structural body is larger than the averagewall thickness [see FIG. 1( c)] of the honeycomb segments 2 bconstituting the outermost peripheral surface. In the present invention,the expression “average wall thickness” means the average thickness ofwalls 6 excluding the peripheral wall of honeycomb segment. In thehoneycomb structural body of the present invention having such aconstitution, the reaction rate at the center having a large wallthickness is suppressed low, and accordingly the maximum temperatureinside the structural body decreases (becomes relatively lower) and thetemperature at the outer portion (of small wall thickness) of thestructural body increases (becomes relatively higher); as a result, theconversion rate, purification efficiency and regeneration efficiency canbe kept at sufficient levels and the temperature distribution in thewhole structural body can be made small. Therefore, the honeycombstructural body of the present invention can provide high efficienciesin conversion rate, purification efficiency, regeneration efficiency,etc., and shows an improved durability against breakage caused bythermal stress.

In the present invention, the expression “honeycomb segment notconstituting the outermost peripheral surface of honeycomb structuralbody” (this segment is hereinafter called inner segment) means, in, forexample, FIG. 1( a), two honeycomb segments 2 a not constituting theoutermost peripheral surface 23 of a honeycomb structural body 1; andthe expression “honeycomb segment constituting the outermost peripheralsurface of honeycomb structural body” (this segment is hereinaftercalled outer segment) means four honeycomb segments 2 b constituting theoutermost peripheral surface 23 of the honeycomb structural body 1.Accordingly, at least one inner segment means, in, for example, FIG. 1,one or two segments of the two inner segments 2 a; and at least oneouter segment means one, two, three or four segments of the four outersegments 2 b. In the present invention shown in, for example, FIG. 1,the average thickness of the partition walls 10 in at least one segmentof the four outer segments 2 b is smaller than the average thickness ofthe partition walls 10 in at least one segment of the two inner segments2 a. In the present invention, it is preferred that the average wallthickness of the two inner segments 2 a is larger than the average wallthickness of the four outer segments 2 b.

FIG. 2 shows another embodiment of the present invention. In this case,four central honeycomb segments 2 c having a square section are innersegments; and eight honeycomb segments 2 f, eight honeycomb segments 2 eand four honeycomb segments 2 d (total twenty honeycomb segments) areouter segments. Therefore, the average wall thickness of at least onesegment of the inner segments 2 c is made larger than the average wallthickness of at least one segment of the outer segments 2 f, 2 d and 2e.

The honeycomb segments 2 c of larger average wall thickness is preferredto be located near the center of the honeycomb structural body 1. In,for example, FIG. 2, the average wall thickness of the four innersegments 2 c contacting with the sectional center of the honeycombstructural body 1 is larger than the average wall thickness of one, morepreferably all of the total twenty outer segments 2 f, 2 d and 2 e.

The ratio of the average wall thickness of outer segments of small wallthickness to the average wall thickness of inner segments of large wallthickness is preferably 0.2 to 0.9, more preferably 0.3 to 0.9, and mostpreferably 0.5 to 0.8. When the ratio is too small, production of such ahoneycomb structural body is substantially difficult; when the ratio istoo close to 1, the intended effect of the present invention isunobtainable.

The sectional area of inner segment(s) of large wall thickness ispreferably 9% or more, more preferably 16% or more, and furtherpreferably 25% or more of the whole sectional area of the honeycombstructural body. In the present invention, the expression “sectionalarea” means the area (including through-holes) of a sectionperpendicular to the through-holes, such as shown in FIGS. 1( a), 1(b)and 1(c) or FIG. 2. When this sectional area is too small, the effect ofthe large wall thickness at inner segment(s) is insufficient. Thesectional area of inner segment(s) of large wall thickness is preferably81% or less, more preferably 64% or less, and further preferably 49% orless of the whole volume of the honeycomb structural body. When thissectional area is too large, reductions in reaction efficiency, etc.,take place, which is not preferred.

In FIGS. 1( a), 1(b) and 1(c) and FIG. 2, the cell density (the numberof through-holes per unit sectional area) is the same in the innersegments and the outer segments. However, in the present invention, thecell density may be different in the inner segments and the outersegments, and the cell density of the inner segment(s) of large wallthickness is preferred to be the same as or smaller than the celldensity of the outer segment(s) of small wall thickness. In the presentinvention, the cell density of inner and outer segments is preferably0.9 to 310 cells/cm² (6 to 2,000 cells/in.²). When the cell density isless than 0.9 cell/cm², the geographical surface area is insufficient.When the cell density is more than 310 cells/cm², the pressure loss istoo large. The sectional shape (cell shape) of the through-holes 6 ofthe honeycomb segment 2 is preferably any of a triangle, a tetragon anda hexagon from the standpoint of production of honeycomb segment.

The honeycomb structural body 1 of the present invention is obtained bybonding honeycomb segments 2 into one piece. It can be obtained, forexample, by bonding side surfaces 4 of each two adjacent honeycombsegment using an adhesive 7. It is also preferred to provide a materialA having compressive elasticity between side surfaces of each twoadjacent honeycomb segments. It is also preferred to, as shown in FIGS.1( a), 1(b) and 1(c), provide a material A 3 having compressiveelasticity, more preferably a ceramic fiber-made mat, between thesurfaces 4 ab of inner segment 2 a and outer segment 2 b. It is alsopreferred to, as shown in FIG. 2, provide a material A3 havingcompressive elasticity between the side surfaces 4 ee of two adjacentouter segments 2 e. By thus providing a material A having compressiveelasticity between side surfaces, the thermal stress of a honeycombstructural body is relaxed and the durability of the honeycombstructural body is further enhanced.

In the present invention, the material A having compressive elasticityis preferred to have heat resistance and cushioning. As the compressiveelasticity material A having heat resistance and cushioning, there is anon-intumescent material containing substantially no vermiculite or alow-intumescent material containing a small amount of vermiculite. Sucha material is preferred to contain, as a main component, a ceramic fibermade of at least one kind selected from the group consisting of alumina,high alumina, mullite, silicon carbide, silicon nitride, zirconia andtitania, or of a composite thereof. Of these, a non-intumescent materialcontaining substantially no vermiculite and composed mainly of aluminaor mullite is more preferred. Further, the material A having compressiveelasticity is preferred to be a mat made of such a fiber, and theceramic fiber-made mat is preferred to be a non-intumescent mat composedmainly of alumina or mullite. Further preferably, these ceramic-mademats have a sealing property for prevention of the wetting ofto-be-treated fluid. Preferred specific examples of the material Ahaving compressive elasticity are 1100HT™ produced by 3M Co. and Maftec™produced by Mitsubishi Chemical Corporation.

In the present invention, each honeycomb segment 2 is preferred tocontain, as a main component, (1) at least one kind of ceramic selectedfrom the group consisting of silicon carbide, silicon nitride,cordierite, alumina, mullite, zirconia, zirconium phosphate, aluminumtitanate, titania and combinations thereof, and (2) Fe—Cr—Al, nickel, ormetallic Si and SiC, from the standpoints of the strength, heatresistance, etc., of the honeycomb segment. In the present invention,“main component” means a substance which is 80% or more of allcomponents and which becomes a main crystalline phase. The adhesive 7can as well be selected from among the above-mentioned materialssuitable for a honeycomb segment.

The section of the honeycomb segment 2 has preferably at least one sideof 30 mm or more, more preferably 50 mm or more, and most preferably 70mm or more, for easy arrangement of the material A having compressiveelasticity in production of the honeycomb structural body.

FIG. 3 is a schematic sectional view of a honeycomb structural assembly8 obtained by holding a honeycomb structural body shown in FIG. 1( a),1(b) and 1(c), in a metallic container 11. The honeycomb structuralassembly 8 of the present invention, as shown in FIG. 3, is obtained byproviding a material B having compressive elasticity, on the outermostperipheral surface 23 of a honeycomb structural body 1 in a compressedstate and thereby compression-holding the honeycomb structural body 1 ina metallic container 11.

In the present invention, the material B having compressive elasticityis preferred to have heat resistance and cushioning, similarly to theabove-mentioned material A having compressive elasticity, and is furtherpreferred to have sealing property. The material B having compressiveelasticity may be a non-intumescent material or an intumescent material.The material B having compressive elasticity is preferred to be, forexample, a ceramic fiber composed mainly of at least one kind selectedfrom the group consisting of alumina, high alumina, mullite, siliconcarbide, silicon nitride, zirconia and titania, or of a compositethereof, and is further preferred to be a mat made of such a fiber.Specifically, there can be used, for example, 1100HT™ produced by 3M Co.and Maftec™ produced by Mitsubishi Chemical Corporation, both mentionedabove. There can also be used, for example, Interlam Mat™ produced by 3MCo. (an intumescent mat).

In the present invention, as the method for accommodating a honeycombstructural body 1 and a material B having compressive elasticity in ametallic container 11 in a compressed state, there are suitably used astuffing method shown in FIG. 4, using a guide 17; a tourniquet methodshown in FIG. 5, which comprises winding a metallic plate 11 c round ahoneycomb structural body, pulling the plate to impart a pressure to theouter surface of the honeycomb structural body, and welding and fixingthe to-be-jointed areas of the metallic plate 11 c; and a clamshellmethod shown in FIG. 6, which comprises interposing a honeycombstructural body between two metallic container parts 11 a and 11 b witha load being applied to the parts 11 a and 11 b, and welding theto-be-bonded areas (flanges) 16 a and 16 b of the parts 11 a and 11 b toobtain a honeycomb structural body/metallic container integratedmaterial. There is also suitably used a method (a swaging method)utilizing metal plastic processing, shown in FIG. 7, which comprisesapplying a compression force to a metallic container 11 from the outsidevia a tap (of pressure type) to squeeze the outer diameter of themetallic container 11. There can also be used a method shown in FIG. 8,which comprises squeezing, by plastic processing, the outer surface of ametallic container 11 using a processing jig 18 with the metalliccontainer 11 being rotated, that is, a method which comprises squeezingthe outer diameter of a metallic container by rotary forging and therebyimparting a pressure to the outer surface of a honeycomb structural bodyaccommodated in the metallic container.

When the honeycomb structural body or honeycomb structural assembly ofthe present invention is used as a carrier for catalyst in an internalcombustion engine, a boiler, a chemical reactor, a fuel cell reformer,or the like, the honeycomb segments used therein are allowed to loadthereon a metal having a catalytic activity. As representative metalshaving a catalytic activity, there are mentioned Pt, Pd, Rh, etc. It ispreferred that at least one kind selected from these metals is loaded onthe honeycomb segments.

Meanwhile, when the honeycomb structural body or honeycomb structuralassembly of the present invention is used as a filter for capturing andremoving the particulate substance contained in an exhaust gas, forexample, as a diesel particulate filter (DPF), it is preferred that thecells of the honeycomb structural body are plugged alternately at eachend face of structural body and the partition walls of the honeycombstructural body are used as a filter.

When an exhaust gas containing a particulate substance is taken into ahoneycomb structural body constituted by honeycomb segments, from itsone end face, the exhaust gas enters the inside of the honeycombstructural body from those holes not plugged at the one end face, passesthrough porous partition walls having a filtration ability, and isdischarged from those holes not plugged at the other end face. Theparticulate substance is captured by the partition walls at the time ofits passing through the partition walls. The material used for pluggingan end face of honeycomb segment can be selected from theabove-mentioned materials suitable for the honeycomb segment 2.

As the amount of particulate substance captured and deposited onpartition walls increases, a sudden increase in pressure loss takesplace, a load on the engine increases, and a reduction in fuelconsumption and drivability occurs; hence, the deposited particulatesubstance is burnt and removed periodically by a heating means such asheater or the like, to regenerate the ability of the filter. In order topromote combustion during regeneration, it is possible to load, on thehoneycomb structural body, the above-mentioned metal having a catalystactivity.

In the present invention, in order to load a catalyst on a honeycombstructural assembly, there can be used a method which comprises holdinga honeycomb structural body 1 in a metallic container 11, to form ahoneycomb structural assembly 8 prior to catalyst loading, and thenloading a catalyst on the honeycomb structural body 1. According to thismethod, the risk of chipping-off or breakage of honeycomb structuralbody 1 during catalyst loading can be prevented. It is also preferredthat when the honeycomb structural body or honeycomb structural assemblyof the present invention is used as a catalytic converter, a catalystcomponent is loaded on a honeycomb segment 2, then a honeycombstructural body 1 is formed, and the structural body is accommodated andheld in a metallic container 11.

The present invention is described in more detail below by way ofExamples. However, the present invention is not restricted to theseExamples.

Incidentally, each of the following honeycomb structural bodies producedin Examples and Comparative Examples is a filter used for capturingdiesel particulate, wherein the through-holes are plugged alternately ateach end face of the honeycomb structural body and the partition wallsfunction as a filter.

EXAMPLE 1

A silicon carbide powder was used as a raw material. Thereto were addedmethyl cellulose, hydroxypropoxyl methyl cellulose, a surfactant andwater to prepare a plastic material. This material was subjected toextrusion molding, and the resulting extrudate was dried using amicrowave and hot air. Then, the holes of the dried extrudate wereplugged alternately at each end face of the extrudate with a sealantmade of the same material as for the honeycomb structural body to beobtained, in such a way that each end face of the extrudate looked acheckerboard pattern. Then, the resulting material was heated fordebindering in a N₂ atmosphere and then fired in an Ar atmosphere, toobtain the outer segment 2 b having a sectional shape of ¼ of a ringhaving a outer diameter of 144 mm and an inner diameter of 73 mm and alength of 152 mm, and the inner segment 2 a having a sectional shape of½ of a circle having a diameter of 72 mm and a length of 152 mm. Thesehoneycomb segments were bonded using an adhesive which was a mixture ofcolloidal silica, an alumina fiber and water, and dried, whereby wasassembled a cylindrical honeycomb structural body 1 having a diameter of144 mm and a length of 152 mm. In the honeycomb structural body 1, eachinner segment 2 a had a wall thickness of 0.43 mm, a cell density of 31cells/cm² and a unit heat capacity of 0.76 J/cm³·° C.; each outersegment 2 b had a wall thickness of 0.38 mm, a cell density of 31cells/cm² and a unit heat capacity of 0.68 J/cm³·° C.; the heat capacityratio of inner and outer segments was 0.89; and the wall thickness ratiowas 0.88. Further, the ceramic fiber-made non-intumescent mat was woundaround the outermost peripheral surface of the honeycomb structural body1, then the resulting material was stuffed in a SUS 409-made metalliccontainer 11 using a tapered jig, to compression-fix the segments toeach other and compression-fix the honeycomb structural body to themetallic container, to obtain a honeycomb structural assembly 8.

EXAMPLE 2

The same operation as in Example 1 was conducted to obtain the honeycombstructural body 1 wherein each inner segment 2 a had a wall thickness of0.53 mm, a cell density of 16 cells/cm² and a unit heat capacity of 0.67J/cm³·° C.; each outer segment 2 b had a wall thickness of 0.38 mm, acell density of 31 cells/cm² and a unit heat capacity of 0.68 J/cm³·°C.; the heat capacity ratio of inner and outer segments was about 1; andthe wall thickness ratio was 0.72. Further, the ceramic fiber-madenon-intumescent mat was wound e around the outermost peripheral surfaceof the honeycomb structural body 1, then the resulting material wasstuffed in a SUS 409-made metallic container 11 using a tapered jig, tocompression-fix the segments to each other and compression-fix thehoneycomb structural body to the metallic container, to obtain ahoneycomb structural assembly 8.

EXAMPLE 3

The same operation as in Example 1 was conducted to obtain a honeycombstructural body 1 wherein each inner segment 2 a had a wall thickness of0.64 mm, a cell density of 16 cells/cm² and a unit heat capacity of 0.78J/cm³·° C.; each outer segment 2 b had a wall thickness of 0.31 mm, acell density of 31 cells/cm² and a unit heat capacity of 0.56 J/cm³·°C.; the heat capacity ratio of inner and outer segments was 0.72; andthe wall thickness ratio was 0.48. Further, the ceramic fiber-madenon-intumescent mat was wound around the outermost peripheral surface ofthe honeycomb structural body 1, then the resulting material was stuffedin a SUS 409-made metallic container 11 using a tapered jig, tocompression-fix the segments to each other and compression-fix thehoneycomb structural body to the metallic container, to obtain ahoneycomb structural assembly 8.

COMPARATIVE EXAMPLE 1

The same operation as in Example 1 was conducted to obtain a honeycombstructural body 1 wherein each of the inner segments and outer segmentshad a wall thickness of 0.38 mm, a cell density of 31 cells/cm² and aunit heat capacity of 0.68 J/cm³·° C.; and the heat capacity ratio ofinner and outer segments and the wall thickness ratio were each 1.Further, the ceramic fiber-made non-intumescent mat was wound around theoutermost peripheral surface of the honeycomb structural body 1, thenthe resulting material was stuffed in a SUS 409-made metallic containerusing a tapered jig, to compression-fix the segments to each other andcompression-fix the honeycomb structural body to the metallic container11, to obtain a honeycomb structural assembly 8.

COMPARATIVE EXAMPLE 2

The same operation as in Example 1 was conducted to obtain a honeycombstructural body 1 wherein each of the inner segments and outer segmentshad a wall thickness of 0.43 mm, a cell density of 31 cells/cm² and aunit heat capacity of 0.76 J/cm³·° C.; and the heat capacity ratio ofinner and outer segments and the wall thickness ratio were each 1.Further, the ceramic fiber-made non-intumescent mat was wound around theoutermost e peripheral surface of the honeycomb structural body 1, thenthe resulting material was stuffed in a SUS 409-made metallic container11 using a tapered jig, to compression-fix the segments to each otherand compression-fix the honeycomb structural body to the metalliccontainer 11, to obtain a honeycomb structural assembly 8.

COMPARATIVE EXAMPLE 3

The same operation as in Example 1 was conducted to obtain a honeycombstructural body 1 wherein each inner segment 2 a had a wall thickness of0.38 mm, a cell density of 47 cells/cm² and a unit heat capacity of 0.81J/cm³·° C.; each outer segment 2 b had a wall thickness of 0.38 mm, acell density of 31 cells/cm² and a unit heat capacity of 0.68 J/cm³·°C.; the heat capacity ratio of inner and outer segments was 0.84; andthe wall thickness ratio was 1. Further, the ceramic fiber-madenon-intumescent mat was wound around the outermost peripheral surface ofthe honeycomb structural body 1, then the resulting material was stuffedin a SUS 409-made metallic container 11 using a tapered jig, tocompression-fix the segments to each other and compression-fix thehoneycomb structural body to the metallic container, to obtain ahoneycomb structural assembly 8.

(Burning and Regeneration Test)

Each of the thus-obtained honeycomb filters (honeycomb structuralassemblies) of Examples 1 to 3 and Comparative Examples 1 to 3 wasallowed to capture 30 g of fine particles emitted from a diesel engine(hereinafter called as soot). The soot deposited on each filter wasburnt using an exhaust gas having an inlet gas temperature of 700° C.,an oxygen content of 10% and a flow rate of 0.7 Nm³/min, and temperaturemeasurement was made at 15 points inside the honeycomb structural body.After the burning test, the weight of each honeycomb filter was measuredto determine its soot regeneration efficiency. Further, the damage ofthe structural body caused by firing and regeneration was observedvisually and using a stereoscopic microscope to examine the presence orabsence of breakage.

The properties of the filters produced in Examples 1 to 3 andComparative Examples 1 to 3 are summarized in Table 1 and the testresults are shown in FIG. 9. In the honeycomb structural body ofComparative Example 1, the inside maximum temperature increased to1,050° C. and breakage occurred. In Comparative Example 2 where the wallthickness was made larger, the maximum temperature inside the honeycombstructural body during regeneration decreased to 850° C. and no damagesuch as cracks was seen in the honeycomb structural body; however, thetemperature at the outer peripheral portion did not increase and thesoot regeneration efficiency was extremely low at 71%. In ComparativeExample 3, although the heat capacity of the inner segments was madelarger, the maximum temperature inside the honeycomb structural body washigh at 1,000° C. and the honeycomb structural body broke. In contrast,in Examples 1 to 3 according to the present invention, the maximumtemperature was suppressed low at 780 to 880° C. and the sootregeneration efficiency was high at 90 to 92%.

TABLE 1 Comparative Examples Examples 1 2 3 1 2 3 Cell structure Inner0.38/ 0.43/ 0.38/ 0.43/ 0.53/ 0.64/ segments 31 31 47 31 16 16 Outer0.38/ 0.43/ 0.38/ 0.38/ 0.38/ 0.31/ segments 31 31 31 31 31 31 Heatcapacity ratio (outer 1 1 0.84 0.89 1 0.72 segments/inner segments) Wallthickness ratio (outer 1 1 1 0.88 0.72 0.48 segments/inner segments)Cell structure: wall thickness (mm)/cells (per cm²)

INDUSTRIAL APPLICABILITY

As described above, in the honeycomb structural body and assemblythereof, of the present invention, the wall thickness of the innerportion was made larger than that of the outer portion and thereby themaximum temperature generated in the structural body was suppressed lowand, moreover, the wall thickness of the outer portion was made smallerthan that of the inner portion and thereby the temperature of the outerperipheral portion increased; as a result, the soot regenerationefficiency was high and accordingly the durability and the efficiencywere high.

1. A honeycomb structural body obtained by bonding, into one piece, aplurality of honeycomb segments each having a plurality of through-holessurrounded by partition walls and extending in the axial direction ofthe segment, wherein an average partition wall thickness of at least onehoneycomb segment not constituting the outermost peripheral surface ofthe honeycomb structural body is larger than an average Partition wallthickness of each honeycomb segment constituting the outermostperipheral surface of the honeycomb structural body.
 2. The honeycombstructural body according to claim 1, wherein a ratio of the averagepartition wall thickness of the honeycomb segments constituting theoutermost peripheral surface to the average partition wall thickness ofthe at least one honeycomb segment not constituting the outermostperipheral surface is 0.2 to 0.9.
 3. The honeycomb structural bodyaccording to claim 1, wherein a sectional area of the at least onehoneycomb segment not constituting the outermost peripheral surface is 9to 81% of a sectional area of the honeycomb structural body.
 4. Thehoneycomb structural body according to claim 1, wherein the honeycombstructural body is an exhaust gas purification filter of an automobile.5. The honeycomb structural body according to claim 1, wherein thehoneycomb structural body is a filter that captures diesel particulate.6. The honeycomb structural body according to claim 1, wherein amaterial A having compressive elasticity is provided at part or thewhole of the spaces between side surfaces of each two adjacent honeycombsegments.
 7. The honeycomb structural body according to claim 6, whereinthe material A having compressive elasticity is a ceramic fiber-mademat.
 8. The honeycomb structural body according to claim 7, wherein theceramic fiber-made mat is a non-intumescent mat composed mainly ofalumina or mullite.
 9. The honeycomb structural body according to claim1, wherein the main component of the honeycomb segment comprises (1) atleast one kind of ceramic selected from the group consisting of siliconcarbide, silicon nitride, cordierite, alumina, mullite, zirconia,zirconium phosphate, aluminum titanate, titania and combinationsthereof, and (2) Fe—Cr—Al nickel, or metallic Si and SiC.
 10. Ahoneycomb structural assembly comprising: a metallic container, ahoneycomb structural body, obtained by bonding, into one piece, aplurality of honeycomb segments having a plurality of through-holessurrounded by partition walls and extending in the axial direction ofthe segment, wherein an average partition wall thickness of at least onehoneycomb segment not constituting the outermost peripheral surface ofthe honeycomb structural body is larger than an average partition wallthickness of each honeycomb segment constituting the outermostperipheral surface of the honeycomb structural body, and a material Bhaving compressive elasticity, wherein the material B having compressiveelasticity is provided on the outermost peripheral surface of thehoneycomb structural body in a compressed state and thereby thehoneycomb structural body is compression-held in the metallic container.11. The honeycomb structural assembly according to claim 10, wherein thematerial having compressive elasticity is a ceramic fiber-made mat. 12.The honeycomb structural assembly according to claim 11, wherein theceramic fiber-made mat is a heat-intumescent mat containing vermiculiteor the non-intumescent mat.
 13. The honeycomb structural assemblyaccording to claim 10, wherein the honeycomb structural assembly is acanned assembly obtained by a stuffing method, a tourniquet method, aclamshell method or a swaging method.
 14. The honeycomb structuralassembly according to claim 10, wherein the honeycomb structuralassembly is obtained by loading a catalyst on honeycomb segments andthen accommodating the catalyst-loaded honeycomb segments in a metalliccontainer.
 15. The honeycomb structural assembly according to claim 10,wherein the honeycomb structural assembly is obtained by accommodatinghoneycomb segments in a metallic container and then loading a catalyston the honeycomb segments.